SENSE OF HEARING. 



auditorius extern us, (Fig. 28, ca ) is a species of tube which 

 Fiy. 28. /rtx, commences at the bottom of a widened part 



ilion, called concha, and buries 

 temporal bone ; it is gaping at 

 ts external extremity ; but ends 

 internally, 

 in a species 

 of membra* 

 nous parti- 

 tion, named 

 in e in brana 



05 C 



na 



am 



/yrrif) ani, 

 drum of the 

 ear, which 

 separates it 

 from the mid- 

 dle ear. 



41. The 

 middle ear 

 is composed 

 of the cavity of the tympanum, and some small accessary parts. 



42. The name of tympanum, (Fig. 28, cai.) is given to a small 

 cavity of irregular form which is hollowed out in the petrous 

 portion of the temporal bone, and which is found to lie between 

 ihe auditory canal and the internal ear. It is filled with air, 

 which gets there through a canal called the Etistachian tube, which 

 opens in the superior part of the pharynx. 



43. The entrance to the tympanum is closed by a very thin 

 partition, which is stretched like the parchment over a drum, and 

 hence the name, tympanum. This membrane serves to facilitate 

 the transmission of sounds from without to the very bottom of 

 the auditory apparatus, and also to moderate the intensity of 



Explanation of Fig. 28 A vertical section of the organ of hearing. p, 

 pavilion of the ear. co. concha. ca. auditory canal. t. tympanum behin 1 

 which is seen the cavity of the tympanum (cai.) te the Eustachian tube. 

 flj. foramen nvale. v the vestibule, /. the cochlea. osc. the semicircular 

 canals these canals and the cochlea constitute the labyrinth or internal ear. 

 na. the auditory or acoustic nerve. r. the petrous bone, that is, a part o. 

 the temporal bone which derives its name from a Greek word signifying, 

 rocky, which has been applied to it from its very remarkable hardness. c. 

 cells in the temporal bone. far. glenoid cavity for the articulation of the 

 lower jaw. am. mastoid apophysisor mastoid process of the temporal bone. 



41. Of what does the middle ear consist? 



42. What is the tympanum ? Where is it situated ? Through what pas. 

 age does air enter the tympanum ? 



43. Of what use is the membrana tympani ? Does it modify sound* ' 



